V-shape recess profile for embedded source/drain epitaxy

ABSTRACT

A semiconductor device includes a semiconductor base. A dielectric isolation structure is formed in the semiconductor base. A source/drain of a FinFET transistor is formed on the semiconductor base. A bottom segment of the source/drain is embedded into the semiconductor base. The bottom segment of the source/drain has a V-shaped cross-sectional profile. The bottom segment of the source/drain is separated from the dielectric isolation structure by portions of the semiconductor base.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/287,972, filed on Jan. 28, 2016, the entire disclosure ofwhich is hereby incorporated herein by reference.

BACKGROUND

The semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs. As this progression takes place, challenges from bothfabrication and design issues have resulted in the development ofthree-dimensional designs, such as fin-like field effect transistor(FinFET) device. A typical FinFET device is fabricated with a thin “fin”(or fin-like structure) extending from a substrate. The fin usuallyincludes silicon and forms the body of the transistor device. Thechannel of the transistor is formed in this vertical fin. A gate isprovided over (e.g., wrapping around) the fin. This type of gate allowsgreater control of the channel. Other advantages of FinFET devicesinclude reduced short channel effect and higher current flow.

However, conventional FinFET devices may still have certain problems.For example, conventional FinFET devices may still suffer from problemssuch as dislocation, surface contamination, and/or leakage current.

Therefore, while existing FinFET devices and the fabrication thereofhave been generally adequate for their intended purposes, they have notbeen entirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a perspective view of a FinFET device as an examplesemiconductor device in accordance with embodiments of the presentdisclosure.

FIGS. 2-5 illustrate perspective views of a FinFET device at variousstages of fabrication in accordance with embodiments of the presentdisclosure.

FIGS. 6-7 are different cross-sectional side views of a FinFET device inaccordance with various embodiments of the present disclosure.

FIG. 8 is a flowchart illustrating a method of fabricating asemiconductor device in accordance with various embodiments of thepresent disclosure.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of theinvention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the sake of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed. Moreover, various features may be arbitrarilydrawn in different scales for the sake of simplicity and clarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

The present disclosure is directed to, but not otherwise limited to, afin-like field-effect transistor (FinFET) device. The FinFET device, forexample, may be a complementary metal-oxide-semiconductor (CMOS) deviceincluding a P-type metal-oxide-semiconductor (PMOS) FinFET device and anN-type metal-oxide-semiconductor (NMOS) FinFET device. The followingdisclosure will continue with one or more FinFET examples to illustratevarious embodiments of the present invention. It is understood, however,that the application should not be limited to a particular type ofdevice, except as specifically claimed.

The use of FinFET devices has been gaining popularity in thesemiconductor industry. Referring to FIG. 1, a perspective view of anexample FinFET device 50 is illustrated. The FinFET device 50 is anon-planar multi-gate transistor that is built on a substrate. A thinsilicon “fin-like” structure (referred to as fin) forms the body of theFinFET device 50. A gate 60 of the FinFET device 50 is wrapped aroundthis fin. Lg denotes a length (or width, depending on the perspective)of the gate 60. A source 70 and a drain 80 of the FinFET device 50 areformed in extensions of the fin on opposite sides of the gate 60. Thefin itself serves as a channel. The effective channel length of theFinFET device 50 is determined by the dimensions of the fin.

FinFET devices offer several advantages over traditional Metal-OxideSemiconductor Field Effect Transistor (MOSFET) devices (also referred toas planar devices). These advantages may include better chip areaefficiency, improved carrier mobility, and fabrication processing thatis compatible with the fabrication processing of planar devices. Thus,it may be desirable to design an integrated circuit (IC) chip usingFinFET devices for a portion of, or the entire IC chip.

However, various FinFET fabrication method is still under development.For example, it is found that there are several disadvantages if theflat-shape of embedded source/drain epi contains no remaining silicon.One disadvantage is that epitaxy directly grown on flat silicon makes iteasy to touch adjacent oxide, which generates dislocation. In addition,this design leads to more damage of solid phase doping (SPD) of Fin,which leads to worse surface contamination. Furthermore, because thereis no silicon remaining (since the epi-layer may be grown on a flatsilicon surface), then no silicon could be doped to prevent leakagecurrent.

The present disclosure involves implementing a V-shape design ofembedded source/drain epi-layer to overcome the problems discussedabove. Referring to FIG. 2, a perspective view of an example FinFETdevice 100 is illustrated. The FinFET device 100 is fabricated over asubstrate, which is not specifically illustrated herein for reasons ofsimplicity. In some embodiments, the substrate includes a dielectricmaterial, for example silicon oxide (SiO₂).

The FinFET device 100 includes a semiconductor layer 110 that is formedon the substrate. In an embodiment, the semiconductor layer 110 includesa crystal silicon material. An implantation process may be performed toimplant a plurality of dopant ions to the semiconductor layer 110. Thedopant ions may include an n-type material in some embodiments, forexample arsenic (As) or phosphorous (P), or they may include a p-typematerial in some other embodiments, for example boron (B), depending onwhether an NMOS or a PMOS is needed. After the implantation process isperformed, a doping concentration level in the semiconductor layer 110is in a range from about 1×10¹⁷ ions/cm³ to about 5×10¹⁹ ions/cm³.

The FinFET device 100 includes a plurality of fin structures 150. Thefin structures 150 may be formed by one or more patterning processes,which may involve using photoresists and/or hard masks to define the finstructures 150. For example, the fin structures 150 may be formed byetching away portions of the layer 110.

The FinFET device 100 includes isolation structures 160 formed in thesemiconductor layer 110. The isolation structures are electricallyisolate the fins 150. The isolation structures 160 may also be referredto as shallow trench isolation (STI) structures. In some embodiments,the isolation structures 160 contain a dielectric material such assilicon oxide or silicon nitride.

The FinFET device 100 includes a plurality of gate structures 200 formedover the semiconductor layer 110 and over the isolation structures 160.The gate structures 200 may be formed by one or more patterningprocesses. For example, a gate electrode material (e.g., polysilicon) isformed over the isolation structures 160. A patterned hard mask isformed over the gate electrode material. The patterned hard maskincludes a dielectric layer 210 and a dielectric layer 220. In someembodiments, the dielectric layer 210 may contain silicon nitride, andthe dielectric layer 220 may contain silicon oxide. The patterned hardmask is then used to pattern (e.g., by one or more etching processes)the polysilicon material below to form the gate structures 200. As isshown in FIG. 2, the gate structures 200 are each formed to wrap aroundthe fin structures 150. It is also understood that the gate structures200 may include a gate dielectric layer formed below the gate electrodematerial, but this is not specifically illustrated for the sake ofsimplicity.

Still referring to FIG. 2, a sealing layer 230 is formed over theisolation structures 160, the fin structures 150, and the gatestructures 200. In some embodiments, the sealing layer 230 containssilicon carbon oxynitride (SiCON). In other embodiments, the sealinglayer 230 contains silicon oxycarbide (SiOC).

Referring now to FIG. 3, a process 300 is performed to form recesses320. The recesses 320 are formed by etching the portions of the finstructures 150 that are not wrapped under the gate structures 200 (e.g.,portions of the fin structures 150 disposed between and on either sideof the gate structures 200). As a result of the etching process 300, thefin structures 150 are etched away and are replaced by the recesses 320,and the recesses 320 also extend downwardly into the semiconductor layer110. In some embodiments, the etching process 300 include a dry etchingprocess or dry etching+wet etching (e.g., NH₄OH) processes. Theconfigurable dry etching process parameters include carrier gas (e.g.,NF₃/CL₂, HBr/He, etc.), process temperature, and plasma power.

The etching process 300 is specifically configured so that a uniqueprofile is achieved for each of the recesses 320. In more detail, therecesses 320 each have a cross-sectional profile that becomes narrowerthe further it extends into the semiconductor layer 110. In other words,the cross-sectional profile for each of the recesses is such that it iswider at its top and narrower at its bottom. In some embodiments, thecross-sectional profile resembles a letter “V”. In some otherembodiments, the cross-sectional profile may take on a different shape,as long as a substantial majority of the side surfaces of the recesses320 are surfaces of the semiconductor layer 110 and are free of being indirect physical contact of the isolation structures 160. Alternativelystated, the surfaces of the recesses 320 are from the semiconductorlayer 110.

This unique profile is configured to avoid dislocation defects in asubsequent epitaxial growth process. For example, in an epitaxial growthprocess discussed below, an epi-layer is grown in each of the recesses320 (on the exposed surfaces of the semiconductor layer 110). Thisepi-layer may serve as the source/drain of the FinFET device 100. Thus,the epitaxial growth should be as defect-free as possible to ensure highquality source/drain formation, which would improve the performance ofthe FinFET device 100. However, if the etching process 300 had not beenspecifically configured to achieve the unique cross-sectional profilefor the recesses 320, then the etching process would have exposed asubstantial or significant portion of the side surfaces of the isolationstructures 160. When this occurs, the epitaxial growth process performedsubsequently may encounter problems.

For example, the isolation structures 160 contain a dielectric materialsuch as silicon oxide, which is not a crystal structure. A crystalmaterial cannot be formed directly on the exposed surfaces of theisolation structures 160. As such, the epitaxially grown layer (grownfrom the semiconductor layer 110) in the recesses 320 may suffer fromdislocation issues due to the incompatibility with the isolationstructures 160. These dislocation issues may lower the yield of theFinFET fabrication, and/or worsen the device performance. Anotherpossible negative effect is damage of layer of solid phase doping on theFinFET device.

In comparison, the present disclosure achieves a profile for therecesses 320 such that the recesses 320 mostly expose the surfaces ofthe semiconductor layer 110, rather than exposing the surfaces of theisolation structures 160. As such, the epitaxial growth processsubsequently performed can have improved growth quality, since theepi-layer does not need to be in direct physical contact with the(non-crystal) isolation structures 160. This eliminates or reduces thedislocation defect that otherwise plagues conventional FinFETfabrication, since conventional FinFET fabrication processes either donot specifically tune the etching process parameters to form the uniqueprofile of the recesses 320 (i.e., their recesses would look quitedifferent from the recesses 320 herein), or lack the etching process toform a recess altogether. Therefore, the FinFET device 100 formedaccording to the various aspects of the present disclosure has improveddevice quality and performance compared to conventional FinFET devices.

FIGS. 4-5 provide more detailed 3-dimensional illustrations of a portionof the FinFET device 100 before and after the epitaxial growth process,so as to better illustrate the various aspects of the present disclosurediscussed above. In more detail, FIG. 4 generally corresponds with FIG.3, but it is shown in more detail (i.e., more “zoomed-in”). For reasonsof clarity and consistency, the same elements appearing in FIGS. 2-5 arelabeled the same. As is shown in FIG. 4, the recesses 320 are formed bythe etching process 300 (discussed above with reference to FIG. 3) toexpose portions of the semiconductor layer 110. The recesses 320 eachhave a profile such that it is wider at the top becomes narrower towardthe bottom, for example resembling a letter “V”. The surfaces of therecesses 320 are formed mostly by the exposed portions of thesemiconductor layer 110, and not by the surfaces of the isolationstructure 160.

Referring now to FIG. 5, an epi-layer component 340 is formed via anepitaxial growth process. The epi-layer component 340 is grown from theexposed surfaces of the semiconductor layer 110 (exposed by the recesses320). In some embodiments, the epi-layer component 340 contains silicongermanium (SiGe). In some other embodiments, the epi-layer component 340contains silicon phosphide (SiP). The epi-layer component 340 fills therecesses 320, and thus it may be said that the epi-layer component hasbottom portions or segments that take on (or inherit) the shape and/orprofile of the recesses (e.g., V-shaped). The remaining portion of theepi-layer component 340—located above these V-shaped bottom portions—hasa cross-sectional profile that protrudes laterally outward near themiddle. It is understood that the epi-layer component 340 may serve as asource/drain of the FinFET device 100. Since the profile of the recesses320 allows the epi-layer component 340 to be formed with minimaldislocation defects (e.g., due to it not being in direct physicalcontact with the isolation structures 160), the performance of theFinFET device 100 is enhanced.

FIG. 6 is a fragmentary cross-sectional side view of a portion of theFinFET device 100, so as to illustrate the unique profile of the recessand the epi-layer component 340 in more detail. Again, for reasons ofclarity and consistency, the same elements appearing in FIGS. 2-6 arelabeled the same.

In FIG. 6, the portions of the epi-layer component 340 filling therecesses 320 discussed above are labeled as portions or segments 340A.It may be said that the portions 340A of the epi-layer component are“embedded” in the semiconductor layer 110 (the portions 340A may beinterchangeably referred to as the embedded epi-layer segments 340hereinafter). For example, these embedded epi-layer segments 340A extenddownwardly into the semiconductor layer 110, while being surroundedlaterally by the semiconductor layer 110. These embedded epi-layersegments 340 are also separated from one another horizontally byportions of the isolation structure (labeled as 160A) that are locatedin the semiconductor layer 110. In other words, a respective one of theisolation structures 160A (e.g., containing a dielectric material suchas silicon oxide) is disposed between each adjacent pair of embeddedepi-layer segments 340A. Meanwhile, the rest of the epi-layer component340 (or the remaining portion) is disposed above the portions 340A andabove the semiconductor layer 110 or the isolation structure 160.

In some embodiments, a substantial majority (e.g., at least 90%) of thesurfaces (e.g., sidewall surfaces) of the portions 340A of the epi-layercomponent are free of being in direct physical contact with theisolation structures 160. In other words, most (or all) of the sidewallsurfaces of the embedded portions 340A of the epi-layer component arenot contiguous with the sidewall surfaces of the isolation structures160 or 160A.

In some embodiments, the cross-sectional profile of the embeddedepi-layer segments 340A is V-shaped (i.e., resembling the letter V). Forexample, each embedded epi-layer segment 340A is wider at its top andbecomes narrower the further it extends into the semiconductor layer. Alateral dimension 350 defines the maximum width of the embeddedepi-layer segment 340A. In some embodiments, the lateral dimension 350may be measured from the point (or interface) of the epi-layer component340 that comes into direct contact with the isolation structures 160 or160A on either side. The lateral dimension 350 may also be referred toas a critical dimension of a fin (mathematically expressed as Fin_CD)for the FinFET device 100. Meanwhile, a vertical dimension 360 definesthe depth of each embedded epi-layer segment 340A. The verticaldimension 360 may be measured from a bottommost tip of the embeddedepi-layer segment to a line corresponding to where the lateral dimension350 is measured. The vertical dimension 360 may also be mathematicallyexpressed as V_HT.

In some embodiments, the etching process 300 discussed above isconfigured such that the recess is formed to result in a certain ratiorange between the vertical dimension 360 and the lateral dimension 350.For example, in some embodiments, the vertical dimension 360 is greaterthan about of the lateral dimension. This relationship may be alsoexpressed mathematically as V_HT>½*Fin_CD. In some embodiments, V_HT isin a range from about 5 nanometers to about 20 nanometers, and theFin_CD is in a range from about 5 nanometers to about 15 nanometers. Insome embodiments, the embedded epi-layer segment 340A is also formed tohave an upwardly-facing angle 370. For example, the angle 370 may bedefined by the two side walls of the embedded epi-layer segment 340A.The angle 370 may be in a range that is less than about 120 degrees, forexample between 1 degree and 120 degrees. These ranges (both innumerical numbers and in ratios/relationship) are not trivial, butrather is specifically tuned so as to optimize the performance of theFinFET device 100. For example, it ensures that a sufficient amount ofthe epi-layer is embedded in the semiconductor layer 110 for betterepitaxial growth and better device performance.

As discussed above, this unique profile of the embedded epi-layersegments 340A is achieved by specifically configuring the processparameters of the etching process 300 to define the unique profile forthe recesses 320. One benefit of this is the reduced dislocationdefects, since the epi-layer component 340 (e.g., the embedded segments340A) does not need to be in direct contact with the isolationstructures 160, which do not have crystal structures and thus may causethe crystal-structured epi-layer segments 340A to get dislodged. Here,since the epi-layer component 340 does not need to come into directcontact with the isolation structure 160, physical dislocation of theepi-layer segment 340 is unlikely. Another benefit of the unique shapedesign of the embedded epi-layer segment 340A is that there is moreremaining silicon seat (e.g., the surfaces of the semiconductor layer110 exposed by the recesses 320) for better epitaxial growth. Yetanother benefit is that the more available remaining silicon area couldbe doped to prevent leakage current. As a result, the FinFET device 100has better DC/AC device performance in certain applications.

Also as shown in FIG. 6, a plurality of air gaps or air voids 380 aretrapped between the epi-layer component 340 and the isolation structures160A. The formation of the air gaps 380 is a result of the epitaxialgrowth process, where the epi-layer material is grown out of therecesses 320 (but not on the isolation structures 160/160A) and mergetogether upward to form the epi-layer component 340. The merging of theepi-layer material may occur above the isolation structures 160A, andthereby leading to the formation of the air gaps 380. The formation ofthe air gaps 380 offer improvements, as the air gaps 380 reducegate-to-source/drain coupling capacitance. The smaller such capacitanceis, the faster the transistor speed.

The epi-layer component 340 is also formed to have a cross-sectionalprofile such that it protrudes laterally outward in the middle. The topand bottom portions of the epi-layer component 340 are narrower than atthe middle where it protrudes outward. For example, the epi-layercomponent 340 has laterally-protruding portions 390. which is where theepi-layer component has its maximum width. A capping layer 400 is formedon the epi-layer component 340. The capping layer 400 may containsilicon or silicon germanium. The capping layer 400 protects theepi-layer component 340 therebelow.

FIG. 7 illustrates another embodiment of a FinFET device 500. The FinFETdevice 500 is formed using processes similar to those discussed abovethat were used to form the FinFET device 100. However, unlike the FinFETdevice 100, where a single epi-layer component 340 has a plurality ofV-shaped embedded segments 340A, the FinFET device 500 illustrated inFIG. 7 has a plurality of epi-layer components 540 that each have anembedded segment 540A. The rest of the elements that are similar inFinFET devices 100 and 500 are labeled the same for reasons of clarityand consistency. The embodiment of the FinFET device 500 shown in FIG. 7may be a portion of an SRAM (static random-access memory) device.

As is illustrated in FIG. 7, the embedded epi-layer segment 540A has asubstantially similar profile as the embedded epi-layer segment 340A ofthe FinFET device 100 shown in FIG. 6. In other words, each epi-layersegment 540A may be V-shaped or have another shape so long as asubstantial majority of its side surfaces are free of being in directcontact with the isolation structures 160/160A. As discussed above, theshape of the epi-layer segments 540A is determined by an etching process(similar to the etching process 300) used to form recesses having saidshape in the semiconductor layer 110. The epi-layer segments 540A arethereafter grown on the crystal surfaces of the semiconductor layer 110(and thus fill the recesses). The lateral dimension 350 and the verticaldimension 360 of the epi-layer segment 540A may be formed to havesimilar ranges and/or relationships (e.g., ratios therebetween) as thosediscussed above with reference to FIG. 6.

Due to the non-direct contact with the isolation structures 160/160A,the formation of the epi-layer component 540 has better epitaxial growthand reduced dislocation defects. Also due to the greater amount ofsilicon material (e.g., portions of the semiconductor layer 110 thatlaterally surrounds the epi-layer segments 540A) that could be doped toprevent leakage current, the FinFET device 500 demonstrates better DC/ACdevice performance.

A remaining portion of the epi-layer component 540 located above theepi-layer segment 540A has a cross-sectional profile that is somewhatdifferent than that of the epi-layer component 340 of FIG. 6. Forexample, in FIG. 7, the remaining portion of the epi-layer component 540has a cross-sectional profile that resembles a diamond or a football. Inother words, the top and bottom portions of the epi-layer component 540are somewhat pointy, while its middle portion protrudes laterallyoutward.

It is understood that additional fabrication processes may be performedto complete the fabrication of the FinFET device 100 or the FinFETdevice 500. For example, a gate-replacement process may be performed. Ina gate replacement process, the gate structures 200 shown in FIG. 5 maybe dummy gates, which are removed in a subsequent process. A functionalgate is formed to replace each of the removed dummy gates. In someembodiments, the functional gate has a high-k gate dielectric (e.g., adielectric material having a dielectric constant greater than that ofsilicon oxide) and a metal gate electrode. In some embodiments, thehigh-k gate dielectric may contain HfO₂, ZrO₂, Y₂O₃, La₂O₅, Gd₂O₅, TiO₂,Ta₂O₅, HfErO, HfLaO, HfYO, HfGdO, HfAlO, HfZrO, HfTiO, HfTaO, or SrTiO.In some embodiments, the metal gate electrode may contain Al, W, Cu,TiAlN, TaCN, TiN, WN, W or combinations thereof. The details of the gatereplacement process (as well as other additional processes performed tocomplete the fabrication of the FinFET device) are described in U.S.patent application Ser. No. 14/885,115, filed on Oct. 16, 2015, entitled“Method of Tuning Source/Drain Proximity For Input/Output DeviceReliability Enhancement”, the contents of which are hereby incorporatedby reference in its entirety.

FIG. 8 is a flowchart of a method 800 of fabricating a semiconductordevice in accordance with various aspects of the present disclosure. Themethod 800 includes a step 810 of providing a FinFET device. The FinFETdevice includes: a dielectric isolation structure formed in asemiconductor layer, a semiconductor fin structure that protrudes out ofthe semiconductor layer, and a gate that is formed over and wraps aroundthe semiconductor fin structure.

The method 800 includes a step 820 of forming a recess in thesemiconductor fin structure. The recess is formed using an etchingprocess that includes a dry etching component. The recess extends intothe semiconductor layer and has a cross-sectional profile that resemblesa letter V, such that a substantial majority of a side surface of therecess is not in direct contact with the dielectric isolation structure.In some embodiments, the recess is formed such that it defines anupwardly-facing angle that is less than about 120 degrees. In someembodiments, the recess is formed such that a depth of the recess isgreater than about ½ of a width of the recess.

The method 800 includes a step 830 of growing a source/drain of theFinFET component in the recess using an epitaxial growth process. Thesource/drain completely fills the recess and protrudes out of therecess. In some embodiments, the growing the source/drain is performedsuch that a portion of the source/drain that protrudes out of therecesses traps an air gap underneath.

It is understood that additional process steps may be performed before,during, or after the steps 810-830 discussed above to complete thefabrication of the semiconductor device. For example, the first gate andthe second gates may be dummy gates, in which case the method 800 mayinclude a step of replacing the dummy gates with high-k metal gates.Other process steps are not discussed herein for reasons of simplicity.

The present disclosure offers advantages over conventional FinFET andthe fabrication thereof. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. One advantage is that the V-shape designof the embedded source/drain epi components of the FinFET device of thepresent disclosure provides more silicon seat for better epitaxialgrowth. It also eliminates or reduces the dislocation defects due to theepi-layer not being in physical contact with adjacent dielectricmaterial. The V-shape design of embedded source/drain epi-layer alsoprovides more remaining silicon area, which could be doped to preventleakage current, and therefore the FinFET device demonstrates betterDC/AC device performance.

One embodiment of the present disclosure includes a semiconductordevice. The semiconductor device includes a semiconductor layer. Anisolation structure is formed in the semiconductor layer. An epi-layercomponent is formed on the semiconductor layer. The epi-layer componentincludes a first portion that extends into the semiconductor layer. Alateral dimension of the first portion of the epi-layer componentdecreases as the first portion extends further into the semiconductorlayer. A substantial majority of a side surface of the first portion ofthe epi-layer component is free of being in direct contact with theisolation structure.

Another embodiment of the present disclosure includes a semiconductordevice. The semiconductor device includes a semiconductor base. Adielectric isolation structure is formed in the semiconductor base. Asource/drain of a FinFET transistor is formed on the semiconductor base.A bottom segment of the source/drain is embedded into the semiconductorbase. The bottom segment of the source/drain has a V-shapedcross-sectional profile. The bottom segment of the source/drain isseparated from the dielectric isolation structure by portions of thesemiconductor base.

Yet another embodiment of the present disclosure includes a method offabricating a semiconductor device. A FinFET device is provided. TheFinFET device includes: a dielectric isolation structure formed in asemiconductor layer, a semiconductor fin structure that protrudes out ofthe semiconductor layer, and a gate that is formed over and wraps aroundthe semiconductor fin structure. A recess is formed in the semiconductorfin structure. The recess extends into the semiconductor layer and has across-sectional profile that resembles a letter V, such that asubstantial majority of a side surface of the recess is not in directcontact with the dielectric isolation structure. A source/drain of theFinFET device is grown in the recess using an epitaxial process. Thesource/drain fills the recess and protrudes out of the recess.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor layer; an isolation structure formed in the semiconductorlayer; and an epi-layer component formed on the semiconductor layer;wherein: the epi-layer component includes at least one first portionthat extends into the semiconductor layer and a second portion that isdisposed above the at least one first portion; a maximum lateraldimension of the second portion occurs at a region of the second portionthat is located above the isolation structure; a lateral dimension ofthe at least one first portion of the epi-layer component decreases asthe at least one first portion extends further into the semiconductorlayer; and a substantial majority of a side surface of the at least onefirst portion of the epi-layer component is free of being in directcontact with the isolation structure.
 2. The semiconductor device ofclaim 1, wherein the at least one first portion of the epi-layercomponent has a cross-sectional profile that resembles a letter V. 3.The semiconductor device of claim 2, wherein the epi-layer componentdefines an upwardly-facing angle that is less than about 120 degrees. 4.The semiconductor device of claim 1, wherein: the at least one firstportion of the epi-layer component has a depth and a width; and thedepth is greater than about ½ of the width.
 5. The semiconductor deviceof claim 1, wherein the epi-layer component includes a source/drain of aFinFET transistor.
 6. The semiconductor device of claim 1, furthercomprising a silicon capping layer or a silicon germanium capping layerdisposed over the second portion.
 7. The semiconductor device of claim1, wherein: the at least one first portion includes a plurality of firstportions; and the second portion is disposed above the plurality offirst portions.
 8. The semiconductor device of claim 7, wherein: theplurality of first portions are separated from one another by aplurality of dielectric components disposed in the semiconductor layer;and a respective air gap is disposed above each dielectric component andbelow the second portion of the epi-layer component.
 9. Thesemiconductor device of claim 6, wherein a middle part of the secondportion of the epi-layer component protrudes laterally outward.
 10. Asemiconductor device, comprising: a semiconductor base; a dielectricisolation structure formed in the semiconductor base; and a source/drainof a FinFET transistor formed on the semiconductor base; wherein: atleast one bottom segment of the source/drain is embedded into thesemiconductor base; the at least one bottom segment of the source/drainhas a V-shaped cross-sectional profile; the at least one bottom segmentof the source/drain is separated from the dielectric isolation structureby portions of the semiconductor base; the at least one bottom segmentof the source/drain has a vertical dimension and a lateral dimension;and the vertical dimension is greater than about ½ of the lateraldimension.
 11. The semiconductor device of claim 10, wherein theV-shaped cross-sectional profile corresponds to an angle that is lessthan about 120 degrees.
 12. The semiconductor device of claim 10,wherein: the at least one bottom segment includes a plurality of bottomsegments that each have the V-shaped cross-sectional profile; and aremaining segment of the source/drain is disposed over the plurality ofthe bottom segments and over the semiconductor base.
 13. Thesemiconductor device of claim 12, wherein: a plurality of dielectricelements is located in the semiconductor base; the dielectric elementsare each located between a different pair of the bottom segments of thesource/drain, respectively; and a plurality of air gaps are trappedbetween the remaining segment of the source/drain and the dielectricelements.
 14. The semiconductor device of claim 10, wherein a remainingsegment of the source/drain that is disposed above the bottom segment,the remaining segment having a cross-sectional profile that resembles adiamond or a football.
 15. A method of fabricating a semiconductordevice, comprising: providing a FinFET device, wherein the FinFET deviceincludes: a dielectric isolation structure formed in a semiconductorlayer, a semiconductor fin structure that protrudes out of thesemiconductor layer, and a gate that is formed over and wraps around thesemiconductor fin structure; forming a recess in the semiconductor finstructure, the recess extending into the semiconductor layer and havinga cross-sectional profile that resembles a letter V, such that asubstantial majority of a side surface of the recess is not in directcontact with the dielectric isolation structure; growing a source/drainof the FinFET device in the recess using an epitaxial process, whereinthe source/drain fills the recess and protrudes out of the recess; andforming a silicon capping layer or a silicon germanium capping layer onthe source/drain.
 16. The method of claim 15, wherein the recess isformed such that it defines an upwardly-facing angle that is less thanabout 120 degrees.
 17. The method of claim 15, wherein the recess isformed such that a depth of the recess is greater than about ½ of awidth of the recess.
 18. The method of claim 15, wherein the forming therecess comprises an etching process that includes a dry etchingcomponent.
 19. The method of claim 15, wherein the growing thesource/drain is performed such that a portion of the source/drain thatprotrudes out of the recesses traps an air gap underneath.
 20. Thesemiconductor device of claim 10, wherein a region of the source/drainhaving a maximum lateral dimension is located above an upper surface ofthe dielectric isolation structure.